1. Field of the Invention
The present invention relates to an apparatus for pulling single crystal by Czochralski (CZ) method (a Czochralski (CZ) single crystal puller) equipped with a cooler for cooling a pulled single crystal.
Further, the present invention relates to a CZ single crystal puller which is equipped with a cooler for cooling a pulled single crystal and which can smoothly eliminate dislocations from a silicon seed crystal by means of the Dash""s neck method.
The present invention also relates to a CZ single crystal puller which is equipped with a cooler for cooling a pulled single crystal and which can smoothly perform recharging and additional charging operations.
The present invention further relates to a CZ single crystal puller which is equipped with a cooler for cooling a pulled single crystal and a safety mechanism for avoiding hazard, which would result from installation of the cooler.
The present invention further relates to a technique for optimizing requirements for manufacturing a silicon wafer to be produced by the Czochralski (CZ) method.
2. Related Art
As a CZ single crystal puller which pulls a single crystal by means of the Czochralski (CZ) method, a CZ single crystal puller equipped with a cooler to be disposed in a CZ furnace (herein after often called a xe2x80x9cfurnace coolerxe2x80x9d) for cooling a pulled single crystal has recently been employed. Use of such a CZ single crystal puller equipped with a furnace cooler enables a considerable increase in a single-crystal pull rate. Consequently, efficiency in production of a single crystal ingot or wafer can be increased. Hence, the CZ single crystal puller equipped with a furnace cooler is of great significance.
Studies conducted by the present inventors showed that presence of a cooler poses difficulty in eliminating dislocations from a silicon seed crystal when an attempt is made to eliminate dislocations (primarily dislocations induced by thermal shock when a seed crystal is immersed in a melt) from a silicon seed crystal through use of the Dash""s neck method (W. Dash: Journal of Applied Physics 30 (1959) pg. 459).
The present invention has been conceived in light of the foregoing drawbacks, and a first object of the present invention is to provide a CZ single crystal puller which is equipped with a cooler to be disposed in a CZ furnace and which can smoothly eliminate dislocations from a silicon seed crystal by means of the Dash""s neck method.
In addition to the furnace cooler, a thermal insulation shield or a like member for shielding heat radiating from a heater or a melt is often disposed within the CZ furnace in order to optimize requirements for pulling a single crystal.
At the time of pulling of a single crystal through use of the CZ method, material is additionally charged or recharged in order to produce a single crystal of maximum size during a single process.
However, members to be disposed within a furnace (hereinafter often called xe2x80x9cfurnace membersxe2x80x9d); particularly, the cooler and the thermal insulation shield, hinder additional charge or recharge of material. Great attention must be paid to a problem of melt splashes; particularly, during additional charge or recharge of material, rather than during initial charge of material. When a cooler is disposed near a crucible, heating must be effected so as to overcome the cooling effect of the cooler at the time of charge of material. Hence, the amount of energy dissipation is increased.
The present invention has been conceived in view of the above-described drawbacks, and a second object of the present invention is to provide a CZ single crystal puller which is equipped with a cooler and a thermal-insulation shield, both being provided in a CZ furnace, and which can smoothly perform additional charge or recharge of material.
In connection with a CZ single crystal puller which pulls a single crystal by means of the Czochralski (CZ) method, there have already been put forward various types of coolers to be disposed in a CZ furnace of the CZ single crystal puller. One of the proposed coolers moves within the CZ furnace (as described in Japanese Patent Application Laid-Open No. 92272/1999). There is room for improving such a furnace cooler.
The present invention has been conceived in view of the drawback set forth, and a third object of the present invention is to provide a CZ single crystal puller having a cooler which is to be disposed in a CZ furnace and has improved functionality.
A fourth object of the present invention is to provide a CZ single crystal puller which has a cooler moving within a CZ furnace and a safety mechanist, wherein the cooler located within the CZ furnace immediately avoids hazards by means of appropriately detecting potential collision with other furnace members.
In connection with a silicon wafer produced by means of the CZ method for use in manufacturing semiconductor devices, crystalline imperfections which deteriorate the quality of a device are present in the surface layer of a silicon wafer that is simply sliced off from a silicon ingot. As the silicon wafer is subjected to intense heat treatment (i.e., annealing), voids existing in the surface layer of a wafer disappear. For example, it has been known that voidsxe2x80x94which are detected as, for example, LSTDs, FPDs, or COPs, and exist in the surface layer of a CZ silicon wafer having been subjected to hydrogen heat treatment (hydrogen annealing)xe2x80x94disappear and as a result the wafer exhibits a superior oxide film withstand-pressure characteristic (as described in Japanese Patent Publication No. 80338/1991).
However, the effect of hydrogen annealing is limited to solely the area in the vicinity of the uppermost surface of a silicon wafer. In this regard, the present inventors found that the rate at or depth to which defects located in the vicinity of the surface layer of a wafer are eliminated by means of high-temperature annealing substantially depends on the sizes of initial defects. The present inventors have proposed a method of expanding a defect-free area from the surface layer of a wafer to a comparatively deep position in the wafer, by means of increasing a cooling rate of crystal being grown within a temperature zone in which defects are apt to arise (as described in Japanese Patent Application Laid-Open No. 208987/1998), controlling a V/G (V denotes a pull rate, and G denotes a temperature gradient along the crystallographic axis and in the vicinity of a melting point), or controlling the diameter of an OSF ring (as described in Japanese Patent Application Laid-Open No. 154095/2000), thus miniaturizing size of defects in a crystal.
So long as a rate at which a crystal is to be pulled (hereinafter called simply a xe2x80x9ccrystal pull ratexe2x80x9d) is increased, the method enables miniaturization of defects of a growing crystal to a size at which the defects are apt to disappear by means of annealing. Further, if the pull rate is increased, the volume of silicon ingot produced per unit time is eventually increased, thus improving the production efficiency of a wafer.
If a crystal can be pulled faster than what has been expected thus far, the production efficiency of wafers of all types can be improved to a much greater extent, regardless of whether the wafer is to be used for epitaxial growth or annealing purpose.
In a case where a crystal pull rate is increased, if miniaturization of crystalline imperfections becomes possible at least without a crystal being adversely affected by an increase in pull rate, crystalline imperfections can be miniaturized at a high pull rate. Particularly, if an increase in pull rate and miniaturization of crystalline imperfections can be attained simultaneously, immediate production of a wafer for annealing purpose (i.e., from which crystalline imperfections are likely to disappear and which is suitable for undergoing annealing) can be attained.
The present invention has been conceived in view of the drawbacks of the related art set forth, and a fifth object of the present invention is to improve production efficiency of wafers of all types, regardless of whether or not the wafers are to be used for epitaxial growth or annealing purpose, by means of increasing the crystal pull rate.
A sixth object of the present invention is to simultaneous realization of miniaturization of crystalline imperfections to a size smaller than has been expected thus far and an increased pull rate, thereby improving the production efficiency of a wafer for annealing purpose.
To achieve the first object, the present invention provides a Czochralski (CZ) single crystal puller, in which a cooler is moved away from a melt surface during the course of elimination of dislocations from a silicon seed crystal using the Dash""s neck method.
The studies conducted by the present inventors show that, when a thermal insulation member is disposed at a position above a melt surface and a cooling coil is disposed at a position much higher than the location of the thermal insulation member, dislocations can be eliminated only under specific conditions to which the Dash""s neck method is applied. The studies have greatly contributed to completion of the present invention.
A technique analogous to the present invention is described in Japanese Patent Application Laid-Open No. 189488/1999. The application states that elimination of dislocations can be achieved without involvement of a necking process, by means of setting the distance between a melt surface and the lower end of the thermal insulation member to a predetermined range, and reducing the temperature difference between a melt and a seed crystal before immersion into the melt. However, if a cooler is located in the vicinity of a seed crystal, elimination of dislocations is impossible. Examples of inventions in which cooling means is placed at a position higher than a melt for cooling crystal are described in Japanese Patent Application Laid-Open Nos. 317491/1992 and 239291/1996. However, elimination of dislocations after a seed crystal has been immersed in melt is not described at all.
More specifically, in order to achieve the first object, the present invention provides:
(A1) A method of enabling adjustment for eliminating defects by use of the Dash""s neck method, by means of arranging a cooler for cooling a pulled single crystal provided in a Czochralski (CZ) single crystal puller so as to be able to move within a CZ furnace.
(A2) A method of enhancing the efficiency of eliminating dislocation by use of the Dash""s neck method, by means of moving away from a silicon melt surface a cooler which cools a pulled single crystal and is disposed in a CZ silicon single crystal puller so as to be movable within a CZ furnace, during the course of drawing of a seed by use of the Dash""s neck method.
(A3) The method as defined in (A2) is characterized in that a thermal insulation member is moved away from a silicon melt surface along with the cooler.
In the present invention, during the course of drawing of a seed by use of the Dash""s neck method, a cooler and a thermal insulation member are basically spaced apart from the surface of a silicon melt. The locations to which the cooler and the thermal insulation member are retracted are locations where the cooler or the thermal insulation member do not adversely affect elimination of dislocations. Most preferably, the locations belong to a xe2x80x9cdislocation-elimination rangexe2x80x9d (as will be described by reference to the accompanying drawings in a subsequent embodiment, the range can be taken as a given range mapped by the distance between the melt surface and the lower end of the cooler and by the distance between the melt surface and the lower end of the thermal insulation member). When the cooler and the thermal insulation member are situated in the range, there is yielded the same effect as that yielded when the cooler and the thermal insulation member are not provided in the CZ furnace (i.e., the effect of eliminating dislocations by virtue of the Dash""s neck method).
(A4) A method of removing a cooler for cooling a pulled single crystal which is disposed in a CZ silicon single crystal puller, for the purpose of enhancing the efficiency of elimination of dislocations by use of the Dash""s neck method.
(A5) A Czochralski (CZ) single crystal puller having a cooler for cooling a pulled single crystal, and a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, wherein
the hoisting-and-lowering apparatus hoists the cooler to a higher position during the course of drawing of a seed according to the Dash""s neck method.
(A6) A Czochralski (CZ) single crystal puller having a cooler for cooling a pulled single crystal, a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, and a thermal insulation member which surrounds a single crystal and is disposed in the CZ furnace in a portable manner, wherein
the hoisting-and-lowering apparatus hoists the cooler and the thermal insulation member to higher positions during the course of drawing of a seed according to the Dash""s neck method.
(A7) The CZ single crystal puller as defined (A6) is characterized in that the cooler is provided with an engagement member and the thermal insulation member is provided with another engagement member and that, when the cooler is hoisted, the engagement members are engaged with each other, and the thermal insulation member is lifted in association with upward movement of the cooler.
(A8) A Czochralski (CZ) single crystal puller having a crucible which is freely movable in the vertical direction and stores silicon melt and a cooler for cooling a pulled single crystal, wherein
a seed is drawn by use of the Dash""s neck method while the crucible is lowered and the cooler is moved away from the surface of the silicon melt.
(A9) A Czochralski (CZ) single crystal puller having a crucible which is freely movable in the vertical direction and stores silicon melt, a cooler for cooling a pulled single crystal, and a thermal insulation member for surrounding a silicon single crystal pulled from the silicon melt, wherein
a seed is drawn by use of the Dash""s neck method while the crucible is lowered and while the cooler and the bottom surface of the thermal insulation member are moved away from the surface of the silicon melt.
(A10) A silicon ingot produced by the CZ single crystal puller as defined in any one of (A5) to (A9).
(A11) A silicon wafer sliced off from the silicon ingot defined in (A10).
When a wafer is sliced off from a silicon ingot, a wafer is usually sliced off from an area on the silicon ingot to be used for producing products. In contrast, when a wafer is sliced for research purpose or as a dummy, there may be a case where a wafer is sliced off from a shoulder or tail portion of the silicon ingot.
To achieve the second object, the present invention provides a Czochralski (CZ) single crystal puller, wherein a cooler and a thermal insulation member are immediately moved upward away from a melt surface at the time of additional charge or recharge of material.
More specifically, in order to achieve the second object, the present invention provides:
(B1) A method of promoting smooth recharge or additional charge of material, by means of arranging a crucible for melting charged material and a cooler for cooling a pulled single crystal disposed in a Czochralski (CZ) single crystal puller such that the crucible and the cooler are movable within a CZ furnace.
(B2) A Czochralski (CZ) single crystal puller for recharge or additional charge purpose, comprising:
a crucible for melting charged material;
a cooler for cooling a pulled single crystal; and
a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace.
(B3) A Czochralski (CZ) single crystal puller for recharge or additional charge purpose, comprising:
a crucible for melting charged material;
a cooler for cooling a pulled single crystal; and
a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, wherein the hoisting-and-lowering apparatus hoists the cooler so as to move away from material when material is charged.
(B4) The CZ single crystal puller as defined in (B3) further comprises a thermal insulation member which surrounds a single crystal and is disposed in the CZ furnace in a portable manner, wherein the cooler is provided with an engagement member, and the thermal insulation member is provided with another engagement member; and wherein, when the cooler is hoisted, the engagement members are engaged with each other, and the thermal insulation member is lifted in association with upward movement of the cooler.
The expression xe2x80x9cportable statexe2x80x9d means that setting are made such that the thermal insulation member is freely removable and can be moved within the furnace.
(B5) The CZ single crystal puller as defined in (B3) or (B4) is characterized in that a CZ single crystal puller is used for recharging or additional charging purpose.
(B6) The CZ single crystal puller as defined in any one of (B2) through (B5) is characterized in that the cooler is a water-cooling type cooler including a cooling pipe stack which helically surrounds a single crystal and that the engagement member provided in the cooler is a plate member with an engagement section to be inserted into a space between the cooling pipe stack of the cooler.
(B7) The CZ single crystal puller as defined in (B2), (B5), or (B6) is characterized in that a heater for heating the crucible is equipped with a side heater disposed at the side of the crucible and a bottom heater disposed below the crucible.
(B8) The CZ single crystal puller as defined in (B7) is characterized in that the output of the side heater or the output of the bottom heater or both are adjusted in accordance with the amount of melt, as required.
In the CZ single crystal puller according to the present invention, an output of at least one of the side heater and the bottom heater is adjusted, as required, in accordance with the level of melt. Particularly, when a melt is diminished, there can be avoided a problem of an increase in the amount of heat applied to the crucible in order to overcome a cooling effect of the cooler.
As a matter of course, a magnetic field can be applied to the crucible while a side heater and a bottom heater are turned on. Further, application of a magnetic field may or may not be effected while only the bottom heater is turned on. As means for applying a magnetic field to a material melt in the crucible, there can be employed means such as that described in, for example, Japanese Patent Application Laid-Open No. 45889/1981. Further, as means for generating a cusp magnetic field, there can be employed means such as that described in Japanese Patent Application Laid-Open No. 217493/1983.
(B9) A method of curtailing costs for producing a wafer, by use of a CZ single crystal puller for recharge or additional charge purpose defined in (B2), (B5), or (B8).
(B10) A silicon ingot produced by a CZ single crystal puller for recharge or additional charge purpose defined in (B2), (B5), or (B8).
(B11) A silicon wafer sliced off from the silicon ingot defined in (B10).
A silicon ingot manufactured by a CZ single crystal puller for recharge purpose or a CZ single crystal puller for additional charge purpose according to the present invention is longer than that produced by an ordinary CZ single crystal puller, by the amount corresponding to that produced as a result of recharge or additional charge operation. Further, the CZ single crystal puller according to the present invention employs a cooler and enables high-speed pulling of crystal. Hence, the CZ single crystal puller according to the present invention can produce a silicon ingot longer than that produced by the ordinary CZ single crystal puller during the same period of time in which a silicon ingot is produced by the ordinary CZ single crystal puller. For this reason, manufacturing costs can be reduced from those incurred when a silicon ingot is produced by an ordinary CZ silicon crystal puller. Thus, there can be provided a less-expensive silicon ingot or less-expensive silicon wafers.
In a sense, when a less-expensive silicon ingot or a less-expensive silicon water is provided (particularly when the price of a silicon ingot or wafer is far cheaper and cannot be achieved by application of the conventional technology), it can be suggested that the silicon ingot or wafer was produced by means of the CZ single crystal puller for recharge purpose of the CZ single crystal puller for additional purpose according to the present invention. Hence, infringement of the right of the present invention can be suggested.
When a wafer is sliced off from a silicon ingot, a wafer is usually sliced off from an area on the silicon ingot to be used for producing products. In contrast, when a wafer is sliced for research purpose or as a dummy, there may be a case where a wafer is sliced off from a shoulder or tail portion of the silicon ingot.
The silicon wafer production method and CZ single crystal puller according to the present invention are not affected by the type of a single crystal ingot to be pulled. It is thought that the method and puller can be applied to a general CZ method. Hence, a single crystal ingot to be pulled is not limited to a silicon single crystal ingot.
To achieve the third object of the present invention, immediate operation for avoiding hazard is ensured by means of changing the travel speed of the cooler, as required. The travel direction of the cooler is not limited to the vertical direction. Directional variations are added, such as movement in an inclined direction or rotation, whereby a cooler is hoisted so as not to hinder movement or visual recognition of other furnace members.
More specifically, in order to achieve the third object, the present invention provides:
(C1) A Czochralski (CZ) single crystal puller for pulling a single crystal from a melt, having a crucible for storing melt, a crucible hoisting-and-lowering apparatus for hoisting or lowering the crucible, a thermal insulation member for surrounding a pulled single crystal, a heater for supplying heat to the crucible, a cooler for cooling the pulled single crystal, and a cooler movement apparatus for moving the cooler, wherein
the cooler movement apparatus changes a travel speed of the cooler in two or more steps.
Preferably, the cooler movement apparatus is a cooler hoisting-and-lowering apparatus for moving the cooler vertically.
(C2) A Czochralski (CZ) single crystal puller for pulling a single crystal from a melt, having a crucible for storing melt; a crucible hoisting-and-lowering apparatus for hoisting or lowering the crucible; a thermal insulation member for surrounding a pulled single crystal; a heater for supplying heat to the crucible; a cooler for cooling the pulled single crystal; a chamber for storing the crucible, the crucible hoisting-and-lowering apparatus, the thermal insulation member, the heater, and the cooler; and a cooler movement apparatus for moving the cooler, wherein
the cooler includes a cooling pipe stack which surrounds a pulled single crystal, and a supply-and-exhaust pipe which passes through the chamber and supplies cooling water to the cooling pipe stack, and
the cooler movement apparatus includes a bridging member connected to the supply-and-exhaust pipe, a screw-threaded shaft screwed to the bridging member, and a drive member for rotating the screw-threaded shaft.
(C3) The CZ single crystal puller as defined in (C2) further comprises an expansion-and-contraction member which covers an area in the chamber through which the supply-and-exhaust pipe of the chamber passes such that a hermetic state in the chamber is maintained, and expands or contracts in accordance with vertical movement of the supply-and-exhaust pipe.
(C4) The CZ single crystal puller as defined in (C3) is characterized in that the cooler hoisting-and-lowering apparatus moves the cooler in the vertical direction.
(C5) The CZ single crystal puller as defined in (C3) is characterized in that the cooler hoisting-and-lowering apparatus moves the cooler in an inclined direction.
(C6) The CZ single crystal puller as defined in (C5) is characterized in that a plurality of pieces of cooler hoisting-and-lowering apparatus are provided in the chamber and that the cooling pipe stack of the cooler is separated into separated into segments which are to be integrated so as to constitute a cylindrical shape and is equal in number to the cooler hoisting-and-lowering apparatus.
(C7) The CZ single crystal puller as defined in (C4) or (C5) further comprises an encoder for tracing a distance over which the cooler is vertically moved.
(C8) The CZ single crystal puller as defined in any one of (C2) through (C7) further comprises a limiter member for hindering lower movement of the bridging member from a predetermined position of the screw-threaded shaft.
The simplest limiter member is a solid member such as a metal block. Such a solid member may be formed from a limiter switch (LS). The bridging member may be returned upward immediately after contact on the limiter member has been detected.
(C9) The CZ single crystal puller as defined in any one of (C2) through (C8), the cooler hoisting-and-lowering apparatus changes the speed of vertical movement of the cooler in two steps or more.
The CZ single crystal puller according to the present invention can be provided with magnetic field application means for applying a magnetic field to a melt of material stored in a crucible. As means for applying a magnetic field to a material melt in the crucible, there can be employed means such as that described in, for example, Japanese Patent Application Laid-Open No. 45889/1981. Further, as means for generating a cusp magnetic field, there can be applied means such as that described in Japanese Patent Application Laid-Open No. 217493/1983.
The silicon wafer production method and CZ single crystal puller according to the present invention are not affected by the type of a single crystal ingot to be pulled. It is thought that the method and puller can be applied to a general CZ method. Hence, a single crystal ingot to be pulled is not limited to a silicon single crystal ingot.
In order to achieve the fourth object, the present invention provides, as an example, a CZ single crystal puller, in which a touch sensor is formed between a cooler and another member, and collision between the cooler and another member is immediately and accurately detected. On the basis of the result of detection, the cooler is retracted immediately from a dangerous location.
More specifically, in order to achieve the fourth object, the present invention provides:
(D1) A method of enhancing maintainability of a Czochralski (CZ) single crystal puller, by means of arranging a cooler for cooling a pulled single crystal provided in the CZ single crystal puller so as to be able to move within a CZ furnace.
Here, the expression xe2x80x9cmovementxe2x80x9d is abroad concept covering ascending action and descending action. The expression implies curved motion, such as rotational movement, as well as linear motion in the longitudinal, lateral, and slant directions.
(D2) A method of enhancing maintainability of a Czochralski (CZ) single crystal puller equipped with a cooler which can be hoisted and lowered within a CZ furnace and cools a pulled single crystal, wherein, in the event that anomalies have arisen in the CZ single crystal puller, the cooler is retracted from a location where the anomalies have arisen.
It is though that, in most cases, retraction of a cooler from a location where anomalies have arisen is embodied by moving the cooler away from a melt surface or moving the cooler away from a pulled single crystal.
(D3) A method of enhancing maintain ability of a Czochralski (CZ) single crystal puller equipped with a cooler which can be hoisted and lowered within a CZ furnace and cools a pulled single crystal, wherein, in the event that anomalies have arisen in the CZ single crystal puller for reasons of vertical movement of the cooler, the cooler is temporarily moved in the reverse direction.
The expression xe2x80x9ctemporarily moving the cooler in the reverse directionxe2x80x9d means that, if the cooler is in the course of lowering action, the cooler is lifted slightly. In contrast, if the cooler is in the course of ascending action, the cooler is lowered slightly. In the CZ single crystal puller according to the present invention, the upward movement or downward movement of the cooler in this case falls within a range of about 5 mm.
(D4) A method of enhancing maintainability of a Czochralski (CZ) single crystal puller equipped with a cooler which can be hoisted and lowered within a CZ furnace and cools a pulled single crystal, wherein the speed of vertical movement of the cooler is made variable; and wherein, in the event that anomalies have arisen in the CZ single crystal puller, the cooler is retracted from a location where the anomalies have arisen.
(D5) A method of enhancing maintainability of a Czochralski (CZ) single crystal puller equipped with a cooler which can be hoisted and lowered within a CZ furnace and cools a pulled single crystal, wherein the speed of vertical movement of the cooler is made variable; and wherein, in the event that anomalies have arisen in the CZ single crystal puller for reasons of vertical movement of the cooler, the cooler is switched to a high-speed mode and is retracted from a location where the anomalies have arisen.
(D6) The method as defined in any one of (D1) through (D5) is characterized in that the cooler is of water-cooling type.
(D7) A Czochralski (CZ) single crystal puller having a cooler for cooling a pulled single crystal and a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, wherein, in the event that anomalies have arisen in the CZ single crystal puller, the hoisting-and-lowering apparatus hoists the cooler so as to move away from a melt surface.
(D8) The CZ single crystal puller as defined in (D7) is characterized in that the hoisting-and-lowering apparatus variably changes the hoisting or lowering speed of the cooler, and, in the event that anomalies have arisen, the hoisting-and-lowering apparatus is switched to a higher speed and moves the cooler away from a melt surface.
(D9) The CZ single crystal puller as defined in (D7) or (D8) further comprises a thermograph for sensing the distribution of internal temperature of the CZ furnace or a temperature sensor for sensing the temperature of the surface of the cooler, wherein, when an anomalous rise in the surface temperature of the cooler is sensed, the cooler is moved away from a pulled single crystal and material melt.
The xe2x80x9ctemperature sensorxe2x80x9d is essentially provided on the side of the cooler facing a pulled single crystal (i.e., on the interior side of the cooler). However, if the temperature sensor is provided on the exterior side of the cooler, overheating of the thermal insulation member by the heater disposed outside (i.e., the heater for heating the crucible) can also be sensed.
(D10) A Czochralski (CZ) single crystal puller having a cooler for cooling a pulled single crystal and a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, wherein, in the event that near miss or collision between the cooler and another furnace member during the lowering of the cooler is detected, the hoisting-and-lowering apparatus hoists the cooler.
(D11) The Czochralski (CZ) single crystal puller as defined in (D10) is characterized in that the hoisting-and-lowering apparatus vertically moves the cooler at a variable speed and that, in the event that near miss or collision has arisen, the hoisting-and-lowering apparatus is switched to a high speed and hoists the cooler.
(D12) A Czochralski (CZ) single crystal puller having a cooler for cooling a pulled single crystal, a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, and a range sensor for sensing the positional relationship between members, wherein, in the event that near miss or collision between the cooler and pulled single crystal or material melt or between other furnace members is detected by the range sensor, the cooler is retracted from a location where the near miss or collision has been detected.
Near miss or collision between a cooler and melt of material can be detected through use of a so-called melt level sensor (described in, e.g., Japanese Patent Application Laid-Open No. 264779/2000). Further, near miss or collision between a cooler and a pulled single crystal becomes possible when the xe2x80x9crange sensorxe2x80x9d is a two-dimensional sensor. The melt level sensor described in the previously-described Japanese Patent Application Laid-Open No. 264779/2000 also has a two-dimensional sensor function. Hence, the melt level sensor is suitable as a sensor to be attached to the CZ single crystal puller according to the present invention. Here, the two-dimensional sensor includes an embodiment in which the horizontal positional relationship is detected by means of a CCD camera.
(D13) A Czochralski (CZ) single crystal puller having a cooler for cooling a pulled single crystal and a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, wherein a touch sensor is constituted as a whole between the cooler and pulled single crystal or material melt or between other furnace members is detected by the range sensor; and wherein, when the touch sensor has sensed contact, the cooler is retracted from a location where the contact has been sensed.
Here, the expression xe2x80x9cconstitutes a touch sensorxe2x80x9d means that a cooler is insulated from a pulled single crystal; for example, a feeble current is applied to the cooler and crystal while an ammeter is connected to the cooler. Alternatively, a melt of material is insulated from other furnace members, and a feeble current is applied to them while an ammeter is connected to the furnace members.
(D14) A Czochralski (CZ) single crystal puller having a cooler for cooling a pulled single crystal and a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, wherein, in the event that overload has arisen during the course of vertical movement of the cooler, the hoisting-and-lowering apparatus moves the cooler in the direction opposite to that in which the overload is to arise, thereby retracting the cooler away from the location where the overload has arisen.
(D15) A Czochralski (CZ) single crystal puller having a cooler for cooling a pulled single crystal and a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, wherein, in the event that anomalous changes have arisen in the weight of a single crystal during the course of pulling of the single crystal, the cooler is retracted away from the single crystal.
The mechanism described in (D12) through (D15) can be incorporated into the puller described in (D10) or (D11).
(D16) The CZ single crystal puller as defined in any one of (D15) through (D17) is characterized in that the cooler is of water-cooling type.
(D17) The CZ single crystal puller as defined in (D16) further comprises a steam sensor for sensing steam originating from the CZ furnace, wherein, in the event that the steam sensor detects steam, the cooler is moved away from a pulled single crystal or material melt.
(D18) The CZ single crystal puller as defined in (D16) further comprises a thermometer for sensing the temperature of cooling water which has circulated through the cooler, wherein, in the event that an anomalous arise in the temperature of the cooling water has been detected, the cooler is moved away from a pulled single crystal or material melt.
(D19) A Czochralski (CZ) single crystal puller having a cooler for cooling a pulled single crystal, a hoisting-and-lowering apparatus for hoisting or lowering the cooler within a CZ furnace, and an encoder for tracing a distance over which the cooler has been vertically moved, wherein, in the event that near miss or collision between the cooler and material melt or between other furnace members is detected on the basis of a value computed through use of information output from the encoder, the cooler is retracted from a location where the near miss or collision is detected.
In order to achieve the fifth object, the present inventors have pinned down a combination of factors which do not mutually act in a negative manner (and which preferably a combination of factors which act in a positive manner). By means of such a combination, the crystal pull rate is increased to a speed greater than that expected thus far. As a result, production efficiency of wafers of all types is improved without regard to whether wafers are for annealing purpose or epitaxial purpose.
In order to achieve the sixth object, the present inventors have pinned down a combination of factors which enable miniaturization of crystalline imperfections and an increase in pull rate, as in the case where the fifth object has been achieved. By means of such a combination, the crystal pull rate is increased to a speed greater than that expected thus far. As a result, production efficiency of wafers for annealing purpose is improved.
Control of sizes of crystalline imperfections during the course of manufacture of a single crystal by use of the CZ method is delicate, because subtle elements are intertwined with each other. There is no guarantee that the common knowledge obtained without use of a cooler applies directly to a situation in which a cooler is used. Against this backdrop, the present inventors have found that the effect of miniaturizing crystalline imperfections yielded by nitrogen doping is sustained even when a cooler is used. This finding has made a great contribution to completion of the present invention.
In a different manner, in order to solve conventional problems relating to an increase in crystal pull rate, the present invention has provided a group of factors [i.e., an aggregation (or palette) of factors] which pertain to an increase in crystal pull rate and miniaturization of crystalline imperfections and do not involve interference or neutralization. One or two or more factors are selected from the group, and an additive effect, more preferably a synergistic effect, is yielded with regard to an increase in crystal pull rate or miniaturization of crystalline imperfections.
To achieve the fifth and sixth objects, the present invention provides:
(E1) A method of pulling a silicon single crystal by use of a Czochralski (CZ) method, wherein a rate at which a silicon single crystal is to be pulled by use of the CZ method is increased by means of selecting one or more factors from the group comprising adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, disposition and adjustment of a cooler, and application and adjustment of a magnetic field.
(E2) A method of pulling a silicon single crystal by use of a Czochralski (CZ) method, wherein crystal imperfections arising in a silicon single crystal to be pulled using the CZ method are reduced, by means of selecting one or more factors from the group comprising adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, disposition and adjustment of a cooler, application and adjustment of a magnetic field, and adjustment of doping level of nitrogen.
(E3) A method of pulling a silicon single crystal by use of a Czochralski (CZ) method, wherein speeding up of a rate at which a silicon single crystal is to be pulled according to a CZ method and miniaturization of crystal imperfections are achieved simultaneously, by means of disposing and adjusting a cooler, as well as selecting one or more factors from the group comprising application and adjustment of a magnetic field, adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, disposition and adjustment of a thermal insulation member, adjustment of a distance between the bottom of the thermal insulation member and a melt surface, and adjustment of doping level of nitrogen
(E4) A silicon ingot for high-speed production of wafers which is produced according to the method as defined in any one of (E1) through (E3) and miniaturizes crystalline imperfections.
(E5) A wafer for epitaxial growth or annealing purpose which is sliced off from the silicon ingot described in (E4).
(E6) A method of optimizing a rate at which a silicon single crystal is to be pulled according to the CZ method, by means of selecting one or more factors from the group comprising adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, disposition and adjustment of a cooler, application and adjustment of a magnetic field, and adjustment of doping level of nitrogen.
(E7) A computer-readable storage medium having stored thereon two or more data sets which are selected from the group comprising adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, disposition and adjustment of a cooler, and application and adjustment of a magnetic field, at the time of pulling a silicon single crystal by use of a Czochralski (CZ) method.
(E8) A computer-readable storage medium having stored thereon two or more data sets which are selected from the group comprising adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, disposition and adjustment of a cooler, application and adjustment of a magnetic field, and adjustment of doping level of nitrogen, at the time of pulling a silicon single crystal by use of a Czochralski (CZ) method.
(E9) A computer-readable storage medium having stored thereon two or more data sets which are selected, along with data for disposing and adjusting a cooler, from the group comprising adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, disposition and adjustment of a cooler, application and adjustment of a magnetic field, and adjustment of doping level of nitrogen, at the time of pulling a silicon single crystal by use of a Czochralski (CZ) method.
(E10) A program for increasing a rate at which a silicon single crystal is to be pulled according to the CZ method, wherein a computer-readable storage medium has stored thereon one or more programs which are selected from the group comprising adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, adjustment of a cooler, and application and adjustment of a magnetic field.
(E11) A program for miniaturizing crystalline imperfections arising in a silicon single crystal is to be pulled according to the CZ method, wherein a computer-readable storage medium has stored thereon one or more programs which are selected from the group comprising adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, adjustment of a cooler, application and adjustment of a magnetic field, and adjustment of doping level of nitrogen.
(E12) A program for increasing a rate at which a silicon single crystal is to be pulled according to the CZ method and for miniaturizing crystalline imperfections, wherein a computer-readable storage medium has stored thereon one or more programs which are selected, along with data for disposing and adjusting a cooler, from the group comprising adjustment of a hot zone, disposition and adjustment of a thermal shield member, adjustment of a distance between the bottom of the thermal shield member and a melt surface, and adjustment of doping level of nitrogen.
(E13) A silicon single crystal puller having stored therein the storage medium defined in any one of (E7) through (E9) and/or the storage medium as defined in any one of (E10) through (E12).
[Definition of Terms]
In the specification, the expression xe2x80x9cfurnace membersxe2x80x9d means material objects which are present within a CZ furnace. The furnace members comprehensively include a cooler, a thermal insulation member, a single crystal, a crucible, the interior wall surface of the CZ furnace, etc.
The expression xe2x80x9cmaintainabilityxe2x80x9d is a broad concept including the ease of maintenance or safety.
The expression xe2x80x9coccurrence of anomaliesxe2x80x9d implies, for example, detection of anomalies caused by operators, power failures, failures of a vacuum pump, failures of power supply for a heater, damage to furnace members, failures of a cooling-water pump, etc.
The expression xe2x80x9canomalous changes in the weight of pulled single crystalxe2x80x9d means that a weight change of greater than ordinary permissible magnitude has arisen in a single crystal being pulled. Such a change is detected by the load imposed on a motor which pulls the single crystal. The expression xe2x80x9canomalous rise in the temperature of cooling waterxe2x80x9d means that a temperature change of greater than ordinary permissible magnitude has arisen in the cooling water circulating through the cooler. Here, a thermometer to be provided in the cooler may be embodied in any form.
The CZ single crystal puller according to the present invention can be provided with magnetic field application means for applying a magnetic field to a melt of material stored in a crucible. As means for applying a magnetic field to a material melt in the crucible, there can be employed means such as that described in, for example, Japanese Patent Application Laid-Open No. 45889/1981. Further, as means for generating a cusp magnetic field, there can be employed means such as that described in Japanese Patent Application Laid-Open No. 217493/1983.
The silicon wafer production method and CZ single crystal puller according to the present invention are not affected by the type of a single crystal ingot to be pulled; it is thought that they can be applied to a general CZ method. Hence, a single crystal ingot to be pulled is not limited to a silicon single crystal ingot.
The xe2x80x9ctemperature sensorxe2x80x9d is formed from, e.g., a thermocouple. The xe2x80x9csteam sensorxe2x80x9d corresponds to an infrared-ray absorbency measurement sensor for detecting steam by means of changes in the absorbance of infrared rays. Further, the xe2x80x9cinfrared-ray absorbency measurement sensorxe2x80x9d measures the amount of infrared rays absorbed or the ratio of absorption of infrared rays. Further, the xe2x80x9cinfrared-ray absorbency measurement sensorxe2x80x9d is of reflection type or transmission type.
The xe2x80x9cthermal insulation memberxe2x80x9d is to be disposed within a furnace of a CZ single crystal ingot production system for producing a single crystal ingot by use of the CZ method. The thermal insulation member is usually disposed so as to surround a single crystal ingot to be pulled from a melt, thus controlling the amount of heat radiated from a melt or a heater. The thermal insulation member regulates the flow of inactive gas supplied to the CZ furnace, as well as controlling the amount of heat radiated from melt or a heater. The thermal insulation member is also called a xe2x80x9cgas flow sleeve.xe2x80x9d
The xe2x80x9chot zonexe2x80x9d means an area in the CZ furnace which is directly or indirectly affected by the heating action of the heater. In some cases, the xe2x80x9chot zonexe2x80x9d does not include a thermal insulation member. The expression xe2x80x9cadjustment of a hot zonexe2x80x9d means addition, modification, or deletion of a certain member, modification of material or type of a certain member, change of layout of members, addition, change, or deletion of moving state of a certain member, and change of energy status of the hot zone.
The expression xe2x80x9cdistance between the bottom of the thermal insulation member and the surface of a meltxe2x80x9d can be measured by any means, so long as the means can appropriate measure a distance. For example, a melt level sensor described in Japanese Patent Application Laid-Open No. 264779/2000 is preferably used. In reality, the lower end of the thermal insulation member is changed during the course of pulling action, by means of thermal stress. Hence, preferably there is used a sensor, such as that described in Japanese Patent Application Laid-Open No. 264779/2000, which can accurately measure the distance between the lower end of the thermal insulation member and the melt surface.
Throughout the specification, the expression xe2x80x9csingle crystalxe2x80x9d is a broad concept implying ingots, bulks, and wafers.
Throughout the specification, the expression xe2x80x9cadjustmentxe2x80x9d is a broad concept implying changes of any status and change of any variable, such as adjustment of a positional relationship, a geometry, or intensity.
The expression xe2x80x9cnitrogen dopingxe2x80x9d implies doping crystal with nitrogen during growth, by means of introduction of nitrogen gas during the course of growth of a crystal or doping silicon melt with nitrides. There has been put forward a method of applying the effect of miniaturizing defects by use of xe2x80x9cnitrogen dopingxe2x80x9d to production of a wafer for annealing purpose (as described in Japanese Patent Application Laid-Open No. 98047/1998).